Micro-electro-mechanical system (mems) structures and design structures

ABSTRACT

Micro-Electro-Mechanical System (MEMS) structures, methods of manufacture and design structures are disclosed. The method includes forming a Micro-Electro-Mechanical System (MEMS) beam structure by venting both tungsten material and silicon material above and below the MEMS beam to form an upper cavity above the MEMS beam and a lower cavity structure below the MEMS beam.

FIELD OF THE INVENTION

The invention relates to semiconductor structures and methods ofmanufacture and, more particularly, to Micro-Electro-Mechanical System(MEMS) structures, methods of manufacture and design structures.

BACKGROUND

Integrated circuit switches used in integrated circuits can be formedfrom solid state structures (e.g., transistors) or passive wires (MEMS).MEMS switches are typically employed because of their almost idealisolation, which is a critical requirement for wireless radioapplications where they are used for mode switching of power amplifiers(PAs) and their low insertion loss (i.e., resistance). MEMS switches canbe used in a variety of applications, primarily analog and mixed signalapplications. One such example is cellular telephone chips containing apower amplifier (PA) and circuitry tuned for each broadcast mode.Integrated switches on the chip would connect the PA to the appropriatecircuitry so that one PA per mode is not required.

Depending on the particular application and engineering criteria, MEMSstructures can come in many different forms. For example, MEMS can berealized in the form of a cantilever structure. In the cantileverstructure, a cantilever arm (suspended electrode) is pulled toward afixed electrode by application of a voltage. The voltage required topull the suspended electrode to the fixed electrode by electrostaticforce is called pull-in voltage, which is dependent on severalparameters including the length of the suspended electrode, spacing orgap between the suspended and fixed electrodes, and spring constant ofthe suspended electrode, which is a function of the materials and theirthickness. An alternative MEMS structure is a bridge, which has bothends fixed to the wafer.

MEMS can be manufactured in a number of ways using a number of differenttools. In general, though, the methodologies and tools are used to formsmall structures with dimensions in the micrometer scale with switchdimensions of approximately 5 microns thick, 50 microns wide, and 200microns long. Also, many of the methodologies, i.e., technologies,employed to manufacture MEMS have been adopted from integrated circuit(IC) technology. For example, almost all MEMS are built on wafers andare realized in thin films of materials patterned by photolithographicprocesses on the top of the wafer. In particular, the fabrication ofMEMS uses three basic building blocks: (i) deposition of thin films ofmaterial on a substrate, (ii) applying a patterned mask on top of thefilms by photolithographic imaging, and (iii) etching the filmsselectively to the mask.

For example, in MEMS cantilever type switches the fixed electrodes andsuspended electrode are typically manufactured using a series ofconventional photolithographic, etching and deposition processes. In oneexample, before the suspended electrode is formed, a layer ofsacrificial material, e.g., silicon, is deposited under the MEMSstructure, to form a cavity, the MEMS suspended electrode is formed, andsilicon is deposited over the MEMS structure to form a cavity. Thecavity over the MEM is used to support the formation of a cap or lid,e.g., SiO₂/SiN dome, to seal the MEMS structure. However, this posesseveral shortcomings. For example, although silicon is an excellentsacrificial material, PVD silicon has poor conformality and slowthroughput; whereas, CVD silicon has oxygen or other impurities whichprevent venting and also can have poor adhesion. The use of siliconmaterial can also result in undercuts, lid pinning or rubbing, as wellas the need for increased contact forces.

Accordingly, there exists a need in the art to overcome the deficienciesand limitations described hereinabove.

SUMMARY

In a first aspect of the invention, a method comprises forming aMicro-Electro-Mechanical System (MEMS) beam structure by venting bothtungsten material and semiconductor material at least above and belowthe MEMS beam to form an upper cavity structure above the MEMS beam anda lower cavity structure below the MEMS beam.

In another aspect of the invention, a method of forming aMicro-Electro-Mechanical System (MEMS) beam comprises: forming a wiringlayer on a substrate; forming a first tungsten material over thesubstrate; forming a first silicon material over the first tungstenmaterial; forming a MEMS beam over the first silicon material; forming avia through the MEMS beam to expose the first silicon material; forminga second silicon material above the MEMS beam and within the via tocontact exposed portions of the first silicon material; forming secondtungsten material on the second silicon material; forming a lid over thesecond tungsten material; forming at least one vent hole in the lid,exposing a portion of the at least second silicon material; venting thefirst and second tungsten material and the first and second siliconmaterial to form a lower cavity and an upper cavity about the MEMS beam,respectively; and sealing the at least one vent hole.

In yet another aspect of the invention, a structure comprises a cavitystructure with tungsten material extruding within the cavity and arecess formed by removal of silicon material through a venting process.

In another aspect of the invention, a design structure tangibly embodiedin a machine readable storage medium for designing, manufacturing, ortesting an integrated circuit is provided. The design structurecomprises the structures of the present invention. In furtherembodiments, a hardware description language (HDL) design structureencoded on a machine-readable data storage medium comprises elementsthat when processed in a computer-aided design system generates amachine-executable representation of the Micro-Electro-Mechanical System(MEMS) structures, which comprises the structures of the presentinvention. In still further embodiments, a method in a computer-aideddesign system is provided for generating a functional design model ofthe Micro-Electro-Mechanical System (MEMS) structures. The methodcomprises generating a functional representation of the structuralelements of the Micro-Electro-Mechanical System (MEMS) structures.

More specifically, in embodiments of the present invention, a method isprovided in a computer-aided design system for generating a functionaldesign model of a MEMS structure which is embodied on tangible readablemedium and when executed on a computing device generates the followingfunctional representations: a MEMS beam having at least one viaextending therethrough; a layered structure below the MEMS beamcomprising a layer of tungsten material formed below a layer of siliconmaterial; a layered structure above the MEMS beam comprising a layer ofsilicon material within the at least one via in contact with the siliconmaterial below the MEMS beam, and a tungsten material thereabove; a lidformed over the layered structure above the MEMS beam; and a lowercavity and an upper cavity, formed by venting the layered structuresthrough at least one vent hole in the lid.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIGS. 1-5 show structures and respective processing steps in accordancewith aspects of the present invention;

FIG. 6 shows a structure and respective processing steps in accordancewith additional aspects of the present invention;

FIG. 7 shows a structure and respective processing steps in accordancewith additional aspects of the present invention;

FIG. 8 shows a structure and respective processing steps in accordancewith additional aspects of the present invention;

FIG. 9a-9c show structures in accordance with any of the aspects of thepresent invention; and

FIG. 10 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

DETAILED DESCRIPTION

The invention relates to semiconductor structures and methods ofmanufacture and, more particularly, to Micro-Electro-Mechanical System(MEMS) structures, methods of manufacture and design structures. Morespecifically, in embodiments, the present invention relates to a MEMSstructure fabricated using a hybrid tungsten and silicon cavity layerswhere the tungsten and silicon layers are formed in separate steps.There are other semiconductor materials, such as Ge, which haveproperties similar to silicon which can also be used with tungsten.Accordingly, it should be understood by those of ordinary skill in theart that such other semiconductor materials can be exchanged for Si,throughout the present invention.

Advantageously, using tungsten provides for a more planar MEMS lidtopology, e.g., planar MEMS cavity formation. The planar MEMS cavitieswill reduce fabrication issues including, for example, lithographicdepth of focus variability and packaging reliability due to dielectriccracking. The combination of tungsten and silicon material can reduce oreliminate lid pinning or rubbing, as well as the need for increasedcontact forces.

It has been found that the use of tungsten material, alone, for theformation of cavity structures has several disadvantages. For example,it has been found that use of tungsten alone results in many issues,e.g., tungsten adhesion, high wafer bow due to very high tensile stressof CVD tungsten, and venting problems using XeF₂. More specifically,amongst other issues, it has been found that:

tungsten chemical vapor deposition (CVD) processes fail due to lack ofadhesion on the underlying material;

CVD tungsten with a thickness of about 2.5 μm will peel at wafer edge,due to high stress and wafer bow or curvature;

tungsten cannot vent using XeF₂ without the aid of other materialsventing at the same time;

tungsten material requires dense vent hole spacing for venting, i.e.,due to a short lateral XeF₂ path, on the order of 3 μm, resulting in theneed for closely spaced vent holes, such as every 6 μm; and

chemical mechanical polishing (CMP) processes of any kind (tungsten oroxide chemistry) oxidizes tungsten surfaces making it impossible toremove during XeF₂ venting.

The present invention has successfully overcome the above discoveredissues by developing a sacrificial cavity tungsten process which resultin equivalent capacitance and reliability of the MEMS devices ascompared to the use of other materials, e.g., silicon, for thesacrificial cavity. For example, in embodiments, the present inventionavoids the need to CMP tungsten, and eliminates the need for denseplacement of vent holes. By avoiding the CMP process on tungsten, thetungsten will not oxidize thus making it possible to vent the tungstenmaterial with the silicon material.

In addition, the present invention can provide a silicon and tungstenbased MEMS cavity with no or minimal topography or cavity residuals byusing a top layer of tungsten material, or a top layer of a thinlydeposited silicon material that will not form seams. The presentinvention also provides the following advantages:

the capability to provide planer and non-planer lids;

structures that avoid undercut of silicon and lifting of materials(e.g., improved adhesion properties to underlying materials);

non-undercut reactive ion etching (RIE) profile at cavity edge;

a layout designed to provide continual presence of silicon duringtungsten venting, to ensure that tungsten material can be properlyvented;

minimizing or reducing lid pinning by a lateral movement of the MEMSbeam during processing;

the elimination of unacceptable wafer bowing; and/or

the elimination of peeling for tungsten depositions of about 3 μm andless by providing a barrier layer of tungsten formed using a plasmavapor deposition (PVD) process.

In embodiments, the processes of the present invention include differentcombinations of a layered sacrificial cavity structure comprisingsilicon and tungsten. In more specific examples, the present inventionrelates to a MEMS structure and method of forming a MEMS cavity (e.g.,upper cavity) with a first layer of silicon, a layer of tungsten formedupon the first layer of silicon, and, in embodiments, a second layer ofsilicon formed upon the layer of tungsten. These materials can then beremoved by a venting process, e.g., venting the first layer and secondlayer of silicon and the layer of tungsten through vent holes.

In embodiments, the layer of tungsten is vented continually while thesilicon is vented, thus ensuring that no residual tungsten (or aninsignificant amount of tungsten) is left within the formed cavitystructure. The removal of the silicon layers and the tungsten layer(s)may occur in the same process step, e.g., XeF₂ etching process. Inembodiments, the tungsten material advantageously provides a gap fillfor the silicon, as well as the other advantages described herein. Thesilicon material, on the other hand, provides the bulk of materialfilling in the cavity structure. It should be understood that althoughthe present invention is discussed with reference to CVD tungstenprocesses, other materials using CVD or ALD deposition processes arealso contemplated by the present invention, taking into considerationthat such materials should produce volatile fluorine when venting with,for example, XeF₂ etchant chemistry.

FIG. 1 shows a structure and related processing steps in accordance withaspects of the invention. The structure includes, for example, asubstrate 10. The substrate 10, in embodiments, can be any layer of adevice. In embodiments, the substrate 10 is an oxide or other insulatormaterial coated silicon wafer or any substrate known to those of skillin the art. As should be known to those of skill in the art, thesubstrate 10 can be implemented in either an SOI wafer or BULKimplementation, or could be an insulating substrate such as sapphire orsilica glass. The constituent materials of the SOI wafer or BULKimplementation may be selected based on the desired end use applicationof the semiconductor device. For example, the insulation layer, e.g.,BOX, may be composed of oxide, such as SiO₂. Moreover, the activesemiconductor layer can be comprised of various semiconductor materials,such as, for example, Si, SiGe, SiC, SiGeC, etc. The SOI wafer may befabricated using techniques well known to those skilled in the art. Forexample, the SOI wafer may be formed by conventional processesincluding, but not limited to, oxygen implantation (e.g., SIMOX), waferbonding, etc.

An interconnect 12 is provided within the substrate 10. The interconnect12 can be, for example, a tungsten or copper stud formed in aconventionally formed via. For example, the interconnect 12 can beformed using any conventional lithographic, etching and depositionprocesses, known to those of skill in the art for forming studs.

Still referring to FIG. 1, a wiring layer is formed on the substrate 10to form multiple wires 14 using conventional deposition and patterningprocesses. For example, a wiring layer can be deposited on the substrateto a depth of about 0.25 microns; although other dimensions arecontemplated by the present invention. Thereafter, the wiring layer ispatterned to form the wires 14. At least one of the wires 14 a is incontact (direct electrical contact) with the interconnect 12. Inembodiments, the wires 14 can be formed from aluminum; although otherwiring materials are also contemplated by the present invention. Forexample, the wires 14 can be a refractory metal such as Ti, TiN, TaN,Ta, and W, or AlCu, AlCuSi, or Cu, CuMn, amongst other wiring materials.In embodiments, the wires 14 could be cladded with Ti and capped with anantireflective layer TiN, e.g. Ti/Al/Ti/TiN; or cladded in Ta or TaN. Anoptional insulator material 16 is formed on the multiple wires 14 andexposed portions of the substrate 10. In embodiments, the insulatormaterial 16 is an oxide deposited to about 50 nm; although otherdimensions are also contemplated by the present invention.

In FIG. 2, a sacrificial material 18 can be deposited on the insulatormaterial, which is used to form a lower cavity structure. Inembodiments, the sacrificial material 18 is a combination of tungstenmaterial 18 a and silicon material 18 b, which is patterned usingconventional lithographic, reactive ion etching (RIE), and CMP steps. Inembodiments, the sacrificial material 18 can be deposited to a height ofabout 0.1 to 10 μm which is determined by the MEMS gap requirement.

In more specific embodiments, the sacrificial material 18 is acombination of silicon and tungsten which can subsequently beselectively removed using, for example XeF₂ gas, to the insulatormaterial 16 or the wires 14 (if the insulator material 16 is absent). Inembodiments, the sacrificial material 18 comprises a lower tungstenmaterial 18 a and an upper silicon material 18 b. In embodiments, thetungsten material 18 a can be deposited using a combination of aphysical vapor deposition (PVD) process and a chemical vapor deposition(CVD) process to a depth of about 0.3 μm; although other depths arecontemplated by the present invention. The upper silicon material 18 bcan be deposited using a CVD process to a depth of about 2 μm; althoughother depths are contemplated by the present invention. In embodiments,the silicon material 18 b can undergo a chemical mechanical polishing(CMP) with a cleaning.

The lower tungsten material 18 a and upper silicon material 18 b can bepatterned using conventional lithographic and reactive ion etching (RIE)steps, as is known to those of skill in the art. Also, as in any of theembodiments, it should be understood by those of skill in the art thatthere is no oxidation (oxide) material at the interface between tungstenmaterial and the silicon material, at any level of the structure, e.g.,tungsten material 18 a and the silicon material 18 b. An optionaltungsten oxide removal clean, such as HF or CrP acid, could be employed,using a vapor or wet chemical process, to remove the tungsten oxideprior to the silicon deposition. This tungsten oxide removal process canbe performed either ex-situ or in-situ. An in-situ clean would beperformed between the last tungsten and the first silicon depositionwithout breaking vacuum in the deposition tool.

Referring still to FIG. 2, an insulator material (e.g., oxide) 20 isdeposited on the sacrificial material 18. The deposition can be, forexample, a conventional conformal deposition process, e.g., chemicalvapor deposition (CVD), depositing the insulator material 20 to a depthof about 2.3 μm to about 3.3 μm; although other depths are alsocontemplated by the present invention. The insulator material 20 can bepolished, e.g., planarized using a CMP process, to achieve a planarsurface with the sacrificial material 18.

In embodiments, the insulator material 20 can undergo a reverse etch(reverse damascene process). More specifically, a resist can bedeposited on the insulator material 20, which is patterned to form anopening, with the resist edges overlapping with edges of the underlyingsacrificial material 18. That is, the resist will slightly mask theunderlying sacrificial material 18, resulting in a reverse image of thepatterned sacrificial material 18. The insulator material 20 is thenplanarized, e.g., to be planar or nearly planar (e.g., flat or planarsurface) with the underlying sacrificial material 18. That is, inembodiments, the insulator material 20 can be etched to the underlyingsacrificial material 18. This planarization process will also planarizethe underlying sacrificial material 18. The planarization process canbe, for example, a CMP process.

Still referring to FIG. 2, in an optional embodiment, one or moretrenches 22 can be formed in the sacrificial material 18, over wirings14. In embodiments, the trenches 22 can be of constant or varying depthsused to form an array of bumpers for the MEMS beam, sized and shapedaccording to the location on the MEMS beam, e.g., the depth of thetrenches may increase towards an end of a MEMS cantilever beam or,alternatively, a reduced area of the beam structure which is initiallypulled-in during actuation (whether a cantilever beam or a bridge beam).In embodiments, the array of trenches are structured so as to provide apredetermined amount of physical spacing, such as 50 nm, between theMEMS beam and an actuator electrode when a voltage is present on theactuator electrode; or they are positioned so that the grounded and dcbiased actuators never come into physical contact. The array of bumpers(formed by the trenches) can also prevent MEMS beam stiction.

In embodiments, deeper trenches can be formed at an end or mid section(e.g., initial pull-in of the MEMS beam), and can be, e.g., formed to adepth of about 0.3 μm; although other dimensions are contemplated by theinvention depending on the design parameters and, more particularly, theheight of the sacrificial material 18. For example, the depth can rangefrom about 1000 Å to 5000 Å. A capacitor oxide deposition is performedon the exposed surfaces, e.g., on the sacrificial material 18, insulatormaterial 20 and in the trench 22, to form a liner 24. A via 26 can beformed in the insulator material 20 to the underlying wire 14 a, usingconventional lithographic and etching processes.

In FIG. 3, a dielectric material 28 is deposited on the sacrificialmaterial 18, e.g., silicon material 18 b, and insulator layer 20. Inembodiments, the dielectric material 28 forms part or all of a MEMScapacitor dielectric. The dielectric material 28, e.g., oxide, can bedeposited to a height of about 80 nm; although other dimensions arecontemplated by the present invention. A via 30 can be formed in theinsulator layers 20 and 28 to the underlying wire 14 a. The via 30 canbe formed using conventional lithographic, etching, and cleaningprocesses, as known in the art. In embodiments, the via 30 should beused outside of the cavity area, because the oxide etch used tofabricate it would be blocked by the layer 18 if it was placed insidethe silicon cavity.

A subsequent metal layer 32 is formed and patterned on the insulatormaterial 28 and within the via 30. The metal layer 32 will contact withthe wire (electrode) 14 a. In embodiments, the metal layer 32 is used toform the MEMS beam lower electrode. In embodiments, the metal layer 32can be TiN, TiN or W, Ru, Pt, Ir, amongst other materials. Thethicknesses of this and other electrodes and/or wires can vary dependingon the specific design parameters. For example, Ti/AlCu/Ti/TiN layerscould be used with 10 nm, 5000 nm, 10 nm, and 32 nm thickness,respectively, which would form Til₃ under and over the AlCu after 400°C. annealing. Alternatively, the metal layer 32 could be formed from anoble metal, such as Au; or a refractory metal, such as W or Ta; orwithout a Ti—AlCu interface, e.g., Ti/TiN/AlCu/TiN.

Still referring to FIG. 3, an insulator material 34 is conformallydeposited over the metal layer 32. In embodiments, the insulatormaterial 34 is a deposited oxide using any of the methods discussedherein. In embodiments, the insulator material 34 is deposited to aheight of about 0.5 μm to 5 μm, depending on the beam spring constantand oxide to metal thickness ratio requirements. In embodiments, vias 36are formed in the insulator material 34, to expose portions of theunderlying metal layer 32.

An upper electrode (metal layer) 38 is formed and patterned over theinsulator layer 34, and also deposited within the vias 36 to contact thelower electrode (metal layer) 32. In embodiments, the upper electrode 38is formed from the same materials as the lower electrode 32. Forexample, in one exemplary embodiment, the electrodes 32 and 38 arecomposed of. Ti/AlCu/Ti/TiN. The metal volume of the electrodes 32 and38 should preferably be the same or substantially the same in order tobalance the overall volume and stress of the device, and hence not placeundue stresses on the beams of the MEMS structures, as discussed in U.S.application Ser. No. 12/974,854, the contents of which are incorporatedby reference herein in its entirety.

Still referring to FIG. 3, an optional insulator material 40 isdeposited on the upper electrode 38 and exposed portions of theinsulator material 34. In embodiments, the insulator material 40 isdeposited to a thickness of about 80 nm; although other dimensions arealso contemplated by the present invention. To balance the MEMS beam,the insulator material 40 over the MEMS beam should be substantially thesame thickness as the insulator material 28 under the MEMS beam. Acavity via 42 is formed through the insulator materials 28, 34 and 40and electrodes 32 and 38 to the underlying silicon layer 18 a, bypatterning and etching through the materials using known lithography andetching processes. In embodiments, any unwanted oxide, such as a nativeoxide which is formed by exposing the layer 18 b to air, can be cleanedusing, for example, an HF acid, prior to the subsequent materialdeposition.

In FIG. 4, an upper cavity of the MEMS device is formed in accordancewith aspects of the present invention. Specifically, a silicon material18 b′ is deposited on the insulator material 40 and within the via 42,contacting the silicon material 18 b. In embodiments, the siliconmaterial 18 b′ is deposited to a depth of about 3 μm; although otherdimensions are contemplated by the present invention. In embodiments,the silicon deposition process is a conformal process, leaving slightrecess. The silicon material 18 b′ can undergo a cleaning process using,e.g., dilute HF.

Tungsten material 18 a′ is deposited on the silicon material 18 b′. Inembodiments, the tungsten material 18 a′ can be deposited to a thicknessof about 70 nm using a PVD process, followed by a CVD process at about395° C., for example. In embodiments, the CVD process will deposittungsten to a thickness of about 0.45 μm; although other dimensions arecontemplated by the present invention. Also, as shown in FIG. 4, thetungsten will fill the recesses (seams), formed by the conformaldeposition process of the silicon material 18 b′. An optional surfaceclean using, for example, HF, could be performed between the PVD and CVDtungsten depositions to remove tungsten oxide from the surface of thePVD tungsten.

A layer of silicon material 18 b″ is deposited on the tungsten material18 a′ using, for example, a PVD process. In embodiments, the PVD processwill deposit the silicon material 18 b″ to a thickness of about 2 μm;although other thicknesses are also contemplated by the presentinvention. In embodiments, the silicon material 18 b″ can be planarized(e.g., using CMP) and cleaned to remove any CMP slurry residue (e.g.,DHF process). The tungsten material 18 a′ should not be exposed to theoptional silicon CMP process to avoid oxidizing the tungsten surface.The silicon material 18 b′ and 18 b″ should preferably be deposited tosuch a thickness that silicon material remains during the venting of anytungsten material, to ensure that the tungsten material is completely orsubstantially completely removed during cavity formation. Also, as inany of the embodiments, the tungsten material 18 a′ is free of oxide atthe interface between tungsten material and the silicon material, e.g.,silicon material 18 b′ and 18 b″, at any level of the structure.

As further shown in FIG. 4, the layers 18 a′ 18 b′ and 18 b″ can bepatterned using conventional lithography and etching processes, known tothose of skill in the art. An insulator (oxide) material 44 can bedeposited on the silicon material 18 b″ and any exposed insulatormaterial 34, to form a lid. As in any of the embodiments, there can be a10× reduction in or elimination of lid topography using tungsten fillprocesses of the present invention. In embodiments, the insulatormaterial 44 can be deposited to a thickness of about 5 μm or more, andcan be deposited using any conventional CVD process. The insulatormaterial 44 can be planarized, partially planarized or leftunplanarized.

In embodiments, a vent hole 46 is patterned and opened in the lid 44,exposing a portion of the underlying silicon material 18 b″ and, inembodiments, the tungsten material 18 a′. In embodiments, the siliconmaterial 18 b″ should be exposed for venting, regardless of whether thevent hole 46 exposes tungsten material 18 a′. It should be understoodthat more than one vent hole 46 can be formed in the lid 44. The venthole 46 can be formed using conventional lithographic and etchingprocesses known to those of skill in the art. The width and height ofthe vent hole 46 determines the amount of material that should bedeposited after venting to pinch off the vent hole. In general, theamount of material that should be deposited to pinch off the vent hole46 decreases as the vent hole width decreases; and as the vent holeaspect ratio, which is the ratio of the vent hole height to width,increases. In embodiments, a 3 μm thick pre-venting lid would have a 1μm vent hole diameter and the vent hole would be circular, octagonal, orsquare. The vent holes 46 can be formed at several locations, toportions (expose portions) of the silicon material 18 b″. For example,the vent holes 46 can be spaced apart more than 6 μm.

In FIG. 5, the sacrificial layers 18 a, 18 b, 18 b′ 18 b″ and 18 a′ arevented or stripped by way of the vent hole(s) 46. In embodiments, thestructure, and in particular, the exposed underlying sacrificial layer18 b″ can be cleaned with an HF solution prior to venting to remove thenative oxide. In embodiments, the stripping (e.g., venting) can beperformed using a XeF₂ etchant chemistry through the vent hole(s) 46,where the tungsten material is vented at the same time as the siliconmaterial. The etching will strip all of the material (silicon andtungsten) forming an upper cavity or chamber 48 a and a lower cavity orchamber 48 b and a connecting via 48 c, and is selective to many othermaterials, including SiO₂. In embodiments, all or substantially all ofthe tungsten material is removed or vented, prior to the siliconmaterial.

As further shown in FIG. 5, the vent hole 46 can be sealed with amaterial 50, such as a dielectric or metal. Optional layer 52 isdeposited to provide a hermetic seal. The layers 50 and 52 could be, forexample, a 5 micron PECVD SiO₂ film and a 500 nm PECVD silicon nitridefilm or other films known to provide a hermetic seal over material 50.

FIG. 6 shows an alternate structure and respective processing steps inaccordance with aspects of the present invention. In particular, in theembodiment shown in FIG. 6, the structure 100 includes tungsten material18 a″ in the recesses (seams) formed by the deposition processes of thesilicon material 18 b′. In embodiments, the silicon material 18 b′ isdeposited to a depth of about 2.8 μm, using conventional conformaldeposition processes, e.g., CVD. The silicon material 18 b′ is thenoptionally planarized to reduce subsequent tungsten depth. Theplanarization process can be, for example, a CMP, reducing the siliconmaterial 18 b′ by about 0.7 μm; although other dimensions are alsocontemplated by the present invention depending on the dimension of theupper cavity. The silicon material 18 b′ can undergo a cleaning, e.g.,brush cleaning, and a HF or other acid cleaning steps to remove residualCMP slurry and native oxide.

Dielectric layer 101 is deposited and patterned such that only theopenings over the cavity vias 42 are exposed and the dielectric layer(e.g., oxide based material) 101 is subsequently etched and thepatterning resist is removed as is known in the art. Tungsten material18 a″ can be selectively deposited within the recesses (seams) using alow stress CVD tungsten deposition. In embodiments, the tungstenmaterial 18 a″ can be deposited to a thickness of about 2 μm using thelow stress CVD tungsten deposition; although other dimensions are alsocontemplated by the present invention depending on the dimension of theupper cavity. An optional layer of PVD tungsten, e.g., 70 nm, can bedeposited prior to the deposition of the dielectric layer 101, to aidthe selective CVD tungsten deposition process.

As further shown in FIG. 6, the layer 18 b′ can be patterned usingconventional lithography and etching processes, known to those of skillin the art. An insulator (oxide) material 44 can be deposited on thesilicon material 18 b″ and any exposed insulator material 34, to form alid. The insulator material 44 can be planarized, partially planarizedor left unplanarized. In embodiments, the insulator material 44 can bedeposited to a thickness of about 5 μm or more, and can be depositedusing any conventional CVD process. A vent hole 46 is patterned andopened in the lid 44, exposing a portion of the underlying siliconmaterial 18 b′. As in any of the embodiments, more than one vent hole 46can be formed in the lid 44. The vent hole 46 may be circular or nearlycircular or other shapes and sizes as already described herein.

The processes then continue by venting the sacrificial layers 18 a, 18b, 18 b′, and 18 a″ by way of the vent hole 46. In embodiments, thestructure, and in particular, the exposed underlying layer 18 b′ can becleaned with an HF solution prior to venting to remove the native oxide.In embodiments, the stripping (e.g., venting) can be performed using aXeF₂ etchant chemistry through the vent hole 46, where the tungstenmaterial is vented at the same time as the silicon material. The etchingwill strip all of the material (silicon and tungsten) forming an uppercavity or chamber 48 a and a lower cavity or chamber 48 b and aconnecting via 48 c, and is selective to many other materials, includingSiO₂. In embodiments, all or substantially all of the tungsten materialis removed or vented, prior to the silicon material. As described above,the vent hole 46 can be sealed with a material 50 and 52, resulting inthe structure of FIG. 5.

FIG. 7 shows an alternate structure and respective processing steps inaccordance with aspects of the present invention. In particular, in theembodiment shown in FIG. 7, the structure 100′ includes deposition oftungsten material 18 a′″ in the recesses (seams) and over siliconmaterial 18 b′. In embodiments, the silicon material 18 b′ is depositedwithin the vias 36 and 42, using conventional conformal depositionprocesses, e.g., PVD, and then cleaned, as already described herein.Tungsten material 18 a′″ is deposited on the silicon material 18 b′using a PVD tungsten process, followed by a CVD tungsten process. Inembodiments, the tungsten can be deposited to a thickness of about 1.5μm; although other dimensions are also contemplated by the presentinvention depending on the dimension of the upper cavity. The tungstenmaterial 18′″ can then be patterned and etched, leaving tungsten overthe cavity via 42.

As further shown in FIG. 7, the insulator (oxide) material 44 can bedeposited on the tungsten material 18 a′″ and any exposed insulatormaterial 34 and silicon material 18 b′, to form a lid as alreadydescribed herein. For example, in embodiments, the insulator material 44can be deposited to a thickness of about 5 μm or more, and can bedeposited using any conventional CVD process. A vent hole 46 ispatterned and opened in the lid 44, exposing a portion of the underlyingsilicon material 18 b′. In embodiments, another vent hole 46′ ispatterned and opened in the lid 44, exposing a portion of the underlyingtungsten material 18 a′″. In this way, both the silicon material 18 b′and the tungsten material 18 a′″ are exposed for venting. As in any ofthe embodiments, more than one vent hole 46 (46′) can be formed in thelid 44.

The processes then continue by venting the sacrificial layers 18 a, 18b, 18 b′, and 18 a′″ by way of the vent holes 46, 46′. In embodiments,the structure, and in particular, the exposed underlying sacrificiallayer 18 b′ can be cleaned with an HF solution prior to venting toremove the native oxide. In embodiments, the stripping (e.g., venting)can be performed using a XeF₂ etchant chemistry through the vent holes46, 46′, where the tungsten material is vented at the same time as thesilicon material. The etching will strip all of the material (siliconand tungsten) forming an upper cavity or chamber 48 a and a lower cavityor chamber 48 b and a connecting via 48 c, and is selective to manyother materials, including SiO₂, as described with reference to FIG. 5.In embodiments, all or substantially all of the tungsten material isremoved or vented, prior to the silicon material. As described above,the vent hole 46 can be sealed with a material 50 and 52, as shown inFIG. 5.

FIG. 8 shows an alternate structure and respective processing steps inaccordance with aspects of the present invention. In particular, in theembodiment shown in FIG. 8, the structure 100″ includes deposition oftungsten material 18 a″″ in the recesses (seams) and over siliconmaterial 18 b′. In embodiments, the silicon material 18 b′ is depositedwithin the vias 36 and 42, using conventional conformal depositionprocesses, e.g., CVD, and subjected to a planarization and cleaningprocesses as already described herein, e.g., brush cleaning and a HF oracid clean. Tungsten material 18 a″″ is deposited on the siliconmaterial 18 b′ using a PVD tungsten process, followed by a CVD tungstenprocess. In embodiments, the tungsten can be deposited to a thickness ofabout 2.5 μm; although other dimensions are also contemplated by thepresent invention depending on the dimension of the upper cavity. Thesilicon material can undergo a CMP process to remove material from thesurface, e.g., to remove any alumina. The surface of the materials,e.g., silicon material 18 b′ and tungsten material 18 a″″ can undergo aHF or acidic clean, with optional cleans.

As further shown in FIG. 8, the underlying silicon material 18 b′ canoptionally extend beyond at least one edge of the tungsten material 18a″″. This may occur due to a selective deposition process, or aconventional patterning process. In any scenario, the insulator (oxide)material 44 can be deposited on the tungsten material 18 a″″ and anyexposed insulator material 34 and silicon material 18 b′, to form a lid,as already described herein. For example, the insulator layer 44 can bedeposited to a thickness of about 5μm or more, and can be depositedusing any conventional CVD process. A vent hole 46 is patterned andopened in the lid 44, exposing a portion of the underlying siliconmaterial 18 b′. In additional or alternative embodiments, a vent hole46″ can be opened in the lid 44 and through the tungsten material 18a″″, to the underlying silicon material 18 b′. In this alternativeembodiment, the underlying silicon material 18 b′ need not extend beyondedges of the tungsten material 18 a′″. In any of the embodiments, thesilicon material 18 b′ should be exposed for venting, regardless ofwhether the vent holes 46, 46″ expose tungsten material 18 a″″. As inany of the embodiments, more than one vent hole can be formed in the lid44. The vent holes 46, 46″ may be circular or nearly circular or othershapes and sizes as described herein.

The processes then continue by venting the sacrificial layers 18 a, 18b, 18 b′, and 18 a″″ by way of the vent holes 46, 46″. In embodiments,the structure, and in particular, the exposed underlying sacrificiallayer 18 b′can be cleaned with an HF solution prior to venting to removethe native oxide. In embodiments, the stripping (e.g., venting) can beperformed using a XeF₂ etchant chemistry through the vent holes 46, 46″,where the tungsten material is vented at the same time as venting of thesilicon material. The etching will strip all of the material (siliconand tungsten) forming an upper cavity or chamber 48 a and a lower cavityor chamber 48 b and a connecting via 48 c, and is selective to manyother materials, including SiO₂, as shown and described with referenceto FIG. 5. In embodiments, all or substantially all of the tungstenmaterial is removed or vented, prior to the all of silicon materialbeing removed. As described above, the vent holes can be sealed with amaterial 50 and 52, as shown and described with reference to FIG. 5. Thecombined hybrid silicon and tungsten cavity processes described abovecan be used to form the cavity under, over, or both under and over theMEMS beam.

FIGS. 9a-9c show structures in accordance with any of the aspects of thepresent invention. More specifically, FIG. 9a shows the lower silicon1000, middle tungsten 1002, upper silicon 1004, and photoresist 1006layers. Due to etch selectivity differences during a SF6-based reactiveion etch (RIE) process, the silicon layers 1000 and 1002 are undercutmuch more than the tungsten layer 1004 during the post cavity patterningRIE process. This undercut difference is shown in FIG. 9b . FIG. 9cshows a cavity 200 formed by venting tungsten and silicon materials,e.g., Si, W and Si, which exhibited the RIE undercut difference shown inFIG. 9b . As should be understood by those of skill in the art, thecavity can be an upper cavity or lower cavity of a MEMS beam structure.As shown in FIG. 9c , the venting of the silicon material can form arecess or undercut 210 with respect to tungsten material 1002, afterventing.

It should be understood by those of skill in the art that the tungstenmaterial of any of the embodiments is not subjected to a CMP process.Accordingly, oxide will not form on the tungsten material above and/orbelow the MEMS beam. Also, in any of the embodiments, the siliconmaterial can be subjected to a CMP process. For this reason, anymaterial formed on the silicon material, e.g., lid material (insulator44) can have a planar surface. Also, as should be understood by those ofskill in the art, in any of the embodiments described herein, anysubsequently formed layer on an immediately formed previously layerwould be in direct contact with one another.

FIG. 10 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test. FIG. 10 shows a block diagram of anexemplary design flow 900 used for example, in semiconductor IC logicdesign, simulation, test, layout, and manufacture. Design flow 900includes processes, machines and/or mechanisms for processing designstructures or devices to generate logically or otherwise functionallyequivalent representations of the design structures and/or devicesdescribed above and shown in FIGS. 1-9 c. The design structuresprocessed and/or generated by design flow 900 may be encoded onmachine-readable transmission or storage media to include data and/orinstructions that when executed or otherwise processed on a dataprocessing system generate a logically, structurally, mechanically, orotherwise functionally equivalent representation of hardware components,circuits, devices, or systems. Machines include, but are not limited to,any machine used in an IC design process, such as designing,manufacturing, or simulating a circuit, component, device, or system.For example, machines may include: lithography machines, machines and/orequipment for generating masks (e.g. e-beam writers), computers orequipment for simulating design structures, any apparatus used in themanufacturing or test process, or any machines for programmingfunctionally equivalent representations of the design structures intoany medium (e.g. a machine for programming a programmable gate array).

Design flow 900 may vary depending on the type of representation beingdesigned. For example, a design flow 900 for building an applicationspecific IC (ASIC) may differ from a design flow 900 for designing astandard component or from a design flow 900 for instantiating thedesign into a programmable array, for example, a programmable gate array(PGA) or a field programmable gate array (FPGA) offered by Altera® Inc.or Xilinx® Inc.

FIG. 10 illustrates multiple such design structures including an inputdesign structure 920 that is preferably processed by a design process910. Design structure 920 may be a logical simulation design structuregenerated and processed by design process 910 to produce a logicallyequivalent functional representation of a hardware device. Designstructure 920 may also or alternatively comprise data and/or programinstructions that when processed by design process 910, generate afunctional representation of the physical structure of a hardwaredevice. Whether representing functional and/or structural designfeatures, design structure 920 may be generated using electroniccomputer-aided design (ECAD) such as implemented by a coredeveloper/designer. When encoded on a machine-readable datatransmission, gate array, or storage medium, design structure 920 may beaccessed and processed by one or more hardware and/or software moduleswithin design process 910 to simulate or otherwise functionallyrepresent an electronic component, circuit, electronic or logic module,apparatus, device, or system such as those shown in FIGS. 1-9 c. Assuch, design structure 920 may comprise files or other data structuresincluding human and/or machine-readable source code, compiledstructures, and computer-executable code structures that when processedby a design or simulation data processing system, functionally simulateor otherwise represent circuits or other levels of hardware logicdesign. Such data structures may include hardware-description language(HDL) design entities or other data structures conforming to and/orcompatible with lower-level HDL design languages such as Verilog andVHDL, and/or higher level design languages such as C or C++.

Design process 910 preferably employs and incorporates hardware and/orsoftware modules for synthesizing, translating, or otherwise processinga design/simulation functional equivalent of the components, circuits,devices, or logic structures shown in FIGS. 1-9 c to generate a netlist980 which may contain design structures such as design structure 920.Netlist 980 may comprise, for example, compiled or otherwise processeddata structures representing a list of wires, discrete components, logicgates, control circuits, I/O devices, models, etc. that describes theconnections to other elements and circuits in an integrated circuitdesign. Netlist 980 may be synthesized using an iterative process inwhich netlist 980 is resynthesized one or more times depending on designspecifications and parameters for the device. As with other designstructure types described herein, netlist 980 may be recorded on amachine-readable data storage medium or programmed into a programmablegate array. The medium may be a non-volatile storage medium such as amagnetic or optical disk drive, a programmable gate array, a compactflash, or other flash memory. Additionally, or in the alternative, themedium may be a system or cache memory, buffer space, or electrically oroptically conductive devices and materials on which data packets may betransmitted and intermediately stored via the Internet, or othernetworking suitable means.

Design process 910 may include hardware and software modules forprocessing a variety of input data structure types including netlist980. Such data structure types may reside, for example, within libraryelements 930 and include a set of commonly used elements, circuits, anddevices, including models, layouts, and symbolic representations, for agiven manufacturing technology (e.g., different technology nodes, 32 nm,45 nm, 90 nm, etc.). The data structure types may further include designspecifications 940, characterization data 950, verification data 960,design rules 970, and test data files 985 which may include input testpatterns, output test results, and other testing information. Designprocess 910 may further include, for example, standard mechanical designprocesses such as stress analysis, thermal analysis, mechanical eventsimulation, process simulation for operations such as casting, molding,and die press forming, etc. One of ordinary skill in the art ofmechanical design can appreciate the extent of possible mechanicaldesign tools and applications used in design process 910 withoutdeviating from the scope and spirit of the invention. Design process 910may also include modules for performing standard circuit designprocesses such as timing analysis, verification, design rule checking,place and route operations, etc.

Design process 910 employs and incorporates logic and physical designtools such as HDL compilers and simulation model build tools to processdesign structure 920 together with some or all of the depictedsupporting data structures along with any additional mechanical designor data (if applicable), to generate a second design structure 990.

Design structure 990 resides on a storage medium or programmable gatearray in a data format used for the exchange of data of mechanicaldevices and structures (e.g. information stored in a IGES, DXF,Parasolid XT, JT, DRG, or any other suitable format for storing orrendering such mechanical design structures). Similar to designstructure 920, design structure 990 preferably comprises one or morefiles, data structures, or other computer-encoded data or instructionsthat reside on transmission or data storage media and that whenprocessed by an ECAD system generate a logically or otherwisefunctionally equivalent form of one or more of the embodiments of theinvention shown in FIGS. 1-9 c. In one embodiment, design structure 990may comprise a compiled, executable HDL simulation model thatfunctionally simulates the devices shown in FIGS. 1-9 c.

Design structure 990 may also employ a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design data structures). Designstructure 990 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by amanufacturer or other designer/developer to produce a device orstructure as described above and shown in FIGS. 1-9 c. Design structure990 may then proceed to a stage 995 where, for example, design structure990: proceeds to tape-out, is released to manufacturing, is released toa mask house, is sent to another design house, is sent back to thecustomer, etc.

The method as described above is used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed:
 1. A method comprising: forming aMicro-Electro-Mechanical System (MEMS) beam structure comprising:forming a sacrificial material, which is comprised of both tungstenmaterial and semiconductor material, on a substrate; forming the MEMSbeam structure above the tungsten material and the semiconductormaterial; forming both the tungsten material and the semiconductormaterial above the MEMS beam structure; forming a lid over the tungstenmaterial formed above the MEMS beam structure; etching the semiconductormaterial formed above the MEMS beam structure while etching the tungstenmaterial formed above the MEMS beam structure to form an upper cavitystructure above the MEMS beam structure and below the lid; and etchingboth the tungsten material and the semiconductor material below the MEMSbeam structure to form a lower cavity structure above the substrate andbelow the MEMS beam structure, wherein the etching comprises performingan XeF₂ etching process.
 2. The method of claim 1, wherein the etchingand film thicknesses are controlled to ensure that all or substantiallyall of the tungsten material is removed above the MEMS beam structure,prior to the semiconductor material above the MEMS beam structure. 3.The method of claim 1, wherein the semiconductor material is one ofsilicon material and germanium material.
 4. The method of claim 3,wherein the semiconductor material is silicon material, and wherein thetungsten material and silicon material below the MEMS beam structurecomprises forming the tungsten material on the substrate and forming thesilicon material over the tungsten material.
 5. The method of claim 4,wherein the tungsten material and silicon material above the MEMS beamstructure comprises forming the silicon material within a via in contactwith the silicon material below the MEMS beam structure and forming thetungsten material over the silicon material.
 6. The method of claim 5,further comprising forming a vent hole in the lid to expose at least thesilicon material above the MEMS beam structure.
 7. The method of claim6, wherein the tungsten material at least one of above and below theMEMS beam structure is formed by a physical vapor deposition processfollowed by a chemical vapor deposition process.
 8. The method of claim6, further comprising forming an additional silicon material on thetungsten material above the MEMS beam structure.
 9. The method of claim8, further comprising: planarizing the additional silicon material; andforming the lid over the planarized additional silicon material.
 10. Themethod of claim 9, further comprising: forming another vent hole in thelid, exposing the additional silicon material; and etching the tungstenmaterial, silicon material and additional silicon material above andbelow the MEMS beam structure to form the upper cavity and the lowercavity.
 11. The method of claim 6, further comprising forming anothervent hole in the lid to expose the tungsten material above the MEMS beamstructure.
 12. The method of claim 11, wherein the etching and filmthicknesses are controlled to ensure that all or substantially all ofthe tungsten material is removed above the MEMS beam structure throughthe another vent hole, prior to removal of the semiconductor materialabove the MEMS beam structure through the vent hole.
 13. The method ofclaim 1, wherein the lid is formed with a planar surface on an undersidethereof by depositing the lid directly on one of the tungsten materialformed over the MEMS beam structure or another layer of semiconductormaterial formed on the tungsten material formed over the MEMS beamstructure.
 14. The method of claim 1, wherein the sacrificial materialhas a height between 0.1 to 10 μm.
 15. The method of claim 14, whereinthe semiconductor material is formed over the tungsten material to formthe sacrificial material.
 16. The method of claim 15, wherein thetungsten material is formed by a combination of a physical vapordeposition (PVD) process and a chemical vapor deposition (CVD) process,and the semiconductor material is formed by a CVD process.
 17. Themethod of claim 16, wherein the tungsten material is formed to a depthof about 0.3 μm and the semiconductor material is formed to a depth ofabout 0.2 μm.